1. Filed of the Invention
The present of the invention relates to a data reproducing apparatus for reproducing main data from a data read out from a recording medium. More particularly, the present invention relates to a data reproducing apparatus using a memory which stores main data separated from data read out from a recording medium.
2. Background of the Invention
In general, in a recording and/or reproducing apparatus such as a tape recorder, a disc player or the like which records or reproduces digital audio signals or digital video signals on or from a recording medium, recording data has a main data such as digital audio data or digital video data or the like implemented by error correction processing or an interleaving processing and auxiliary data such as address information, control information or the like. For example, in a format of a so-called Compact Disc (CD), audio signals of stereo left and right channels are respectively sampled at 44.1 KHz to implement quantization of 16 bits thereto to form audio PCM signals. The audio PCM signals are provided to implement coding processing thereto using CIRC (Cross Interleave Reed-Solomon Code) to thereby provide the main data. The main data is further added to subcode data as auxiliary data including discrimination information showing whether data exits as music or between music pieces, and information such as the song numbers, an elapsed time of a music piece, an absolute time or the like, to thereby provide recording data to implement modulation based on such data to provide recording signals.
In the case of reproducing the recorded signals on a Compact Disc in the above-described format by using an ordinary reproducing apparatus such as a so-called Compact Disc Player, a clock component is detected from an EFM signal reproduced from the Compact Disc to carry out so-called reproduction of clock. The reproduction of clock is generally carried out by using a PLL (Phase Locked Loop) system. In this case, because the frame frequency of the recording data is 7.35 KHz, and one frame of an EFM recording signal is 588 channel bits, the frequency of the reproduction clock from the PLL system is 4.3218 MHz (=7.35 KHz.times.588). Binary data is taken into the reproducing system of the reproducing apparatus by the PLL system, and demodulation of the EFM signal is carried out. The EFM demodulated data ordinarily undergoes a decoding process including error correction or deinterleaving based on the CIRC by using a RAM for the decoding process. As a result, the EFM demodulated data is converted to a digital audio signal as a linear PCM signal. Data is written into the RAM for the decoding process in synchronism with a reproducing clock of the PLL system and data is read out from the RAM for the decoding process in synchronism with a reference clock generated from a reference oscillator such as a crystal oscillator. The digital audio PCM signal obtained by the decoding process is converted to an analog digital audio signal through a digital to analog (D/A) convertor and a low pass filter (LPF).
Meanwhile, generally in a data reproducing apparatus, particularly in an apparatus including an optical pickup as the above-described CD player, a servo control such as a focusing servo or a tracking servo of the optical pickup may be put out of order by a mechanical disturbance such as an impact, vibration or the like applied to the apparatus. As a result, the data reproducing apparatus fails to carry out normal data reproduction, and any convenience such as a sound break or other disturbance may take place. For this reason, there is provided in a data reproducing apparatus such that a buffer RAM of a relatively large capacity to read out data stored in the buffer RAM to compensate for an interruption of a reproduced signal such as the sound break even in the case where normal data cannot be obtained from the disc recording medium.
The above-described CD player or data reproducing apparatus, is required to read out the data from the buffer RAM in a burst manner where such an interruption occurs. A burst manner means that is read out from the buffer RAM in a predetermined data unit, at a high speed. In writing data into the buffer RAM, it is necessary to control the write address to allow the buffer RAM to store adjacent data in a continuous state. In this case, it is proposed that since an address such as time information is not added to the decoded processed main data as PCM data itself, the time information of subcode serving as auxiliary data is used to carry out write and/or read operations with respect the buffer RAM. In a more practical sense, for example, it is proposed to rotationally drive a disc at a rotational speed about twice or three-four times greater than the standard one to cut or clip data read out from the disc with subcoding frame, that is, block of subcode, length corresponding to 13.3 msec at the time of an ordinary reproduction, being as a unit to write it into the buffer RAM.
However, as above-described, since writing into the RAM for decoding process is executed in synchronism with the reproducing clock of the PLL system including so-called a jitter component owing to the unevenness of the rotation of the disc, whereas read out from the RAM for decoding process is executed by the reference clock from the crystal oscillator, a time difference corresponding to the jitter component exists between write data and read data with respect to the RAM for the decoding process. For this reason, if an attempt is made to carry out the write/read operation into and from the buffer RAM with main data being divided every subcoding frame, divisional points or delimiter points having reproducibility cannot be obtained because of the jitter. As a result, overlap or missing of write data into the buffer RAM may take place by the above-described jitter. That is, in such cases that adjacent main data are connected in the buffer RAM every subcoding frame, delimiter points having reproducibility cannot be provided as above-described, so sound skip and/or overlap of sound may take place.
In view of this, the applicant of this invention has already proposed, in the specification and drawings of the Japanese Patent Application No. 03-25566 from which priority was claimed now issued U.S. Pat. No. 5,237,575, a data reproducing apparatus adapted to reproduce main data obtained by implementing error correction coding process to digital data from the disc on which data including auxiliary information added every predetermined length of the main data is recorded. The data reproducing apparatus has a signal processor, a memory, a controller and a comparator. The signal processor separates the main data from the data read out from the disc and carries out an error correction processing. The memory subsquentially stores output data from the signal processor. The controller continuously outputs data stored in the memory. The comparator compares the data patterns before and after connecting portions of data subjected to the write and/or the read operation with respect to the memory to detect a coincidence. The apparatus continuously reproduces subsequent data at the time of the coincidence according to the compared result of the comparator. In accordance with this apparatus, since an approach is employed to make a comparison between data patterns at connecting portions of dealt in a memory as a RAM to connect subsequent data at the time when they coincide with each other, it is advantageously expected that overlap and/or missing of data will not take place.
In the case of applying the above-mentioned technology to the CD player, an approach is employed to reproduce data of the CD format in which auxiliary subcode information is added along with main PCM audio data subjected to error correction coding processing from the disc on which such data is recorded to control the write and/or read operations into and from the buffer RAM to make, in carrying out the decoding processing of the main data in the reproduced data, comparison between data patterns before and after connecting portions of data subjected to the write and/or read operations in the buffer RAM to detect a coincidence to continuously reproduce subsequent data at the time of coincidence. However, in the case where data interpolation is implemented by a defect formed on the disc or a disturbance or the like or the jitter value is very large by rolling or the like and therefore greatly deviates from a comparison window which is the range from which data patterns to be compared are taken out, coincidence may not hold by the above-described pattern comparison. As a result, continuous reproduction could not be carried out.
In addition, if the width of the comparison window is set to a broad value, in the case where patterns of the same data value continue, data values are apt to take the same value because the level of data is low and the effective bit number is small or in similar cases, there occurs the possibility a connecting error occurs such that data is connected at erroneous portions may take place.